CN109621964B - Nano Na/Fe composite solid acid catalyst and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of biomass utilization, and particularly discloses a nano Na/Fe composite solid acid catalyst, a preparation method and application thereof, wherein the preparation process of the catalyst is as follows: ferrous chloride and ferric chloride are uniformly mixed in a certain proportion under the action of hydrochloric acid, and then sodium hydroxide is dropwise added to prepare the nano Na/Fe composite solid acid catalyst by a forward precipitation method. Mixing the biomass and the prepared nano catalyst in a certain proportion, and pyrolyzing the mixture in an inert atmosphere to obtain a high-selectivity furfural product. The catalyst disclosed by the invention is simple in preparation process, low in cost and high in selectivity, can solve the problems of low furfural selectivity and more byproducts in the prior art, and realizes directional conversion and high-value utilization of biomass.

Description

A kind of nanometer Na/Fe composite solid acid catalyst and its preparation method and application

technical field

The invention belongs to the technical field of biomass utilization, and more particularly relates to a nano-Na/Fe composite solid acid catalyst and a preparation method and application thereof.

Background technique

For a long time, the production of basic chemical products using fossil resources as raw materials has faced the problem of resource shortage, and it has become an inevitable trend to find a clean and renewable alternative new energy source. Biomass energy is the solar energy converted and stored by green plants through photosynthesis, and it is also the only renewable carbon source. It is expected to become one of the important ways to replace fossil energy and solve energy-related problems. my country is very rich in biomass resources, mainly including crop straw, forest waste, industrial organic waste and domestic waste. There are various types of biomass, and its composition is also diverse. In addition to ash, woody biomass is mainly composed of cellulose, hemicellulose and lignin. Among them, cellulose generally accounts for 40-50 wt% of the raw material, and hemicellulose accounts for 30-40 wt% of the raw material. Furfural can be used as the main raw material for organic synthesis, and the production of high-value furfural products by utilizing the abundant biomass resources in my country is of great significance to ensure the sustainable development of our country.

Furfural is one of the important products of rapid pyrolysis of biomass, most of which are generated by the removal of C-6 from a single molecule of glucose, or cellulose first passes through the intermediates of fructofuranose and 5-hydroxymethylfurfural, and then a molecule is removed. Formaldehyde produces furfural. Using furfural as raw material, many derivatives can be prepared by oxidation, condensation and other reactions, and are widely used in synthetic plastics, medicine, pesticides and other industries. Judging from literature reports, most furfural is currently prepared from cellulose or hemicellulose under acid catalysts (inorganic chlorates, molecular sieves, transition metal oxides, acidic metal oxides, etc.), and the catalyst system is not only difficult to recycle. , high corrosiveness, and low catalytic efficiency, unable to obtain furfural products with high selectivity.

Therefore, it is necessary to develop a novel catalyst and method for the directional and efficient conversion of biomass to furfural.

SUMMARY OF THE INVENTION

In view of the above defects or improvement needs of the prior art, the present invention provides a nano-Na/Fe composite solid acid catalyst and a preparation method and application thereof, the purpose of which is to solve the problems of low productivity and low energy consumption in the preparation of furfural by biomass pyrolysis. The current state of selectivity, the catalyst uses magnetic iron oxide particles as the core, and the active groups Na ⁺ /H ⁺ are uniformly dispersed in the surface and internal pores of the protected magnetic iron oxide particles by co-precipitation method. The purpose is to Solve the current situation of low productivity and low selectivity in the preparation of furfural by biomass pyrolysis, solve the problems of low furfural selectivity and many by-products in the prior art, and realize the directional conversion and high-value utilization of biomass , has the advantages of simple preparation process, low cost and high selectivity.

In order to achieve the above object, according to one aspect of the present invention, a method for preparing a nano-Na/Fe composite solid acid catalyst is proposed, which comprises the following steps:

S1 Weigh FeCl ₃ ·6H ₂ O and FeCl ₂ ·4H ₂ O of required quality, put them into deionized water and stir to form a clear solution, add hydrochloric acid and stir;

S2 is gradually dripped with NaOH solution under the stirring of the stirrer to produce red-black precipitation, and the dripping is ended when the pH of the solution is 2-6, and the constant speed stirring is continued, and then it is allowed to stand for a period of time to reduce to room temperature;

The reaction product was recovered by centrifugation in S3, washed with deionized water for several times, and then collected, and then dried in an oven to obtain a nano-Na/Fe composite solid acid catalyst.

As a further preference, in step S1, FeCl ₃ .6H ₂ O and FeCl ₂ .4H ₂ O are prepared according to the mole fraction ratio of Fe ³⁺ :Fe ²⁺ as 2:1, and the amount of deionized water is 200～400ml; hydrochloric acid The concentration is 12mol/L, and the amount of hydrochloric acid added is determined according to the mole fraction ratio of Fe ³⁺ :H ⁺ 1.5:2.

As a further preference, in step S2, the concentration of the NaOH solution is 1mol/L～2mol/L, and the amount of the NaOH solution is prepared with the Na/Fe mass ratio in the total solution as (0.05～2.5):1, and the Na/Fe mass ratio is further preferred is 1.42:1.

As a further preference, in step S2, the stirring temperature is kept at 60° C., the stirring speed is kept at 600-1000 r/min, the stirring time is 1 h after the dropwise addition is completed, and the standing time is 30-60 min.

As a further preference, in step S3, the centrifugal rotation speed is 3000-4000 r/min, and the number of times of washing with deionized water is 2-5 times.

As a further preference, in step S3, the oven temperature is 60° C., and the drying time is 30-60 min.

According to another aspect of the present invention, a nano-Na/Fe composite solid acid catalyst is provided, which is prepared by the method.

According to the last aspect of the present invention, a method for preparing furfural from biomass is provided, which comprises mixing biomass raw materials with the catalyst, placing them in a pyrolysis furnace for pyrolysis, and condensing and collecting the pyrolysis gas to obtain a furfural-enriched product. liquid product.

As a further preference, the pyrolysis reaction is carried out in an inert atmosphere, the pyrolysis temperature is 400-800° C., the heating rate is 200-400° C./min, and the reaction time is 20-30 min.

As a further preference, the biomass raw material is one or more of cellulose, hemicellulose, agricultural waste, and forestry waste, and the ratio of the biomass raw material to the catalyst is 1:10.

In general, compared with the prior art, the above technical solutions conceived by the present invention mainly have the following technical advantages:

1. The present invention uses Na as an auxiliary agent, and prepares catalysts with different shapes under certain conditions through different Na/Fe mass ratios, so as to provide highly active sites for the catalytic pyrolysis of biomass to convert furfural.

2. The present invention obtains the optimal process parameters through further research, so that the Na/Fe mass ratio is 1.42 to prepare a spherical catalyst with a specific surface area as high as 201.4 m ² /g, which can provide a very good solution for the catalytic pyrolysis of biomass for converting furfural. high active site.

3. The nano-Na/Fe composite solid acid catalyst prepared by the present invention exhibits excellent selectivity in the catalytic thermal cracking of biomass, and the furfural selectivity reaches 64.74%. Compared with the previously reported acid catalyst, the selectivity is improved. 20 to 30%.

4. The nano-Na/Fe composite solid acid catalyst prepared by the present invention exhibits more excellent selectivity in the catalytic thermal cracking of hemicellulose, and the furfural selectivity is as high as 99%.

5. The nano-Na/Fe composite solid acid catalyst involved in the present invention has a simple preparation process, cheap and easy-to-obtain raw materials, and the catalyst has magnetism, which is easy to separate and collect, and has a good application prospect.

6. The present invention uses biomass waste as raw material when preparing furfural, which not only turns waste into treasure, but also solves the problem of resource shortage and the problem of pollution discharge.

Description of drawings

Figures 1a-d are the SEM spectra of the Na/Fe composite solid acid catalyst prepared in Examples 1-4, wherein a is the SEM image of the catalyst prepared in Example 1, and b is the catalyst prepared in Example 2 The SEM image of , c is the SEM image of the catalyst prepared in Example 3, d is the SEM image of the catalyst prepared in Example 4, and ◆ in the figure represents the Na/Fe mass ratio in the catalyst;

Fig. 2 is the nitrogen adsorption and desorption curve diagram of the Na/Fe composite solid acid catalyst prepared by embodiment 1-4;

Fig. 3 is the pyrolysis total ion current spectrum of cellulose at 550°C;

Fig. 4 is the total ion current spectrum obtained by pyrolysis after mixing cellulose and Na/Fe solid acid catalyst in a mass ratio of 1:10;

Figure 5 is a total ion chromatogram for qualitative analysis of the pyrolysis product of Example 5 using gas chromatography-mass spectrometry.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as there is no conflict with each other.

The basic principle of the present invention is to first prepare spherical iron oxide with optimized conditions by titration, and control the acidity of the solution by adjusting the Na/Fe ratio, so that the active group Na ⁺ /H ⁺ can be better dispersed on the surface of the oxide carrier; then The prepared catalyst is used in the preparation of high-value furfural by biomass pyrolysis, and the high active acid sites promote the ring cleavage and carbon bond cleavage of biomass such as cellulose and hemicellulose to obtain highly selective target products— furfural.

A method for preparing a nano-Na/Fe composite solid acid catalyst provided by the embodiment of the present invention includes the following steps:

S1 Weigh FeCl ₃ ·6H ₂ O and FeCl ₂ ·4H ₂ O of required mass, put them in deionized water and stir to form a clear solution, add hydrochloric acid and stir, wherein FeCl ₃ ·6H ₂ O and FeCl ₂ ·4H ₂ O is prepared according to the mole fraction ratio of Fe ³⁺ : Fe ²⁺ as 2:1, the concentration of hydrochloric acid is 12mol/L, and the addition of hydrochloric acid is determined by the mole fraction ratio of Fe ³⁺ : H ⁺ as 1.5:2;

S2 is gradually dripped with NaOH solution under the stirring of the stirrer to produce a red-black precipitate, and the dropwise addition is ended when the pH of the solution is 2-6, and the stirring is continued, and then it is allowed to stand for a period of time to reduce to room temperature, wherein the concentration of the NaOH solution is 1mol/ L～2mol/L, the dosage of NaOH solution is prepared with the mass ratio of Na/Fe in the total solution of 0.05～1.5:1, thereby obtaining catalysts with different morphologies; the stirring temperature is kept at 60℃, and the stirring speed is kept at 600-1000r/min , the stirring time is 1h after the dropwise addition is completed, and the standing time is 30-60min. Under the above-mentioned process, the supported Na ions are uniformly dispersed and the catalyst maintains a uniform size;

S3 centrifugally recovers the reaction product and washes it with deionized water for several times, then collects it, and then dries it in an oven to obtain a nano-Na/Fe composite solid acid catalyst. The nano-based catalyst precipitate is separated from the clear liquid. The washing times of deionized water are 2-5 times to wash off excess chloride ions, the oven temperature is 60 ° C, and the drying time is 12-24 h, and the solid acid-like catalyst is obtained under this drying process.

The FeCl ₃ ·6H ₂ O, FeCl ₂ ·4H ₂ O, hydrochloric acid, NaOH, etc. used in the preparation method for preparing the solvent and catalyst raw materials and used in the experiment can be directly purchased from the market.

Through the above method of the present invention, a catalyst with higher specific surface area can be obtained, and the catalyst can provide a high active site for the catalytic pyrolysis of biomass to convert furfural. The use of the catalyst prepared by the invention in the preparation of furfural by catalytic pyrolysis of biomass is specifically as follows: mixing the biomass raw material with the catalyst and placing it in a pyrolysis furnace for pyrolysis, condensing and collecting the pyrolysis gas to obtain a liquid product enriched with furfural, Among them, the pyrolysis reaction is carried out in an inert atmosphere, the pyrolysis temperature is 400-800 °C, the heating rate is 200-400 °C/min, and the reaction time is 20-30 min. Under the action of the solid acid catalyst at the active site, the ring cleavage and carbon bond cleavage of macromolecules such as sugars are promoted, and furfural liquid products are enriched and collected at the condensation device.

Among them, the biomass raw material can be selected from one or more of cellulose, hemicellulose, agricultural waste, and forestry waste, and the ratio of biomass raw material to catalyst is 1:10, so it has a wide range of sources and is clean and sustainable. Biomass can obtain highly selective furfural liquid products through rapid pyrolysis through cheap and readily available solid acid catalysts.

The following are specific embodiments of the present invention.

Example 1

Weigh 31.62 g of ferric chloride hexahydrate and 12.54 g of ferric dichloride tetrahydrate, stir in 150 ml of deionized water to form a clear solution, add 5 ml of 12 mol/L hydrochloric acid dropwise and stir, and then use the forward co-precipitation method. Under the stirring of a magnetic stirrer at 60°C, 1.5mol/L NaOH solution was gradually added dropwise, and a red-black precipitate was formed immediately. The dropwise addition was terminated when the Na/Fe mass ratio of the solution was equal to 1.42, and then continued to maintain a constant speed (800r/min). ) Stir for 1 h, then let stand for about 30 minutes to bring the temperature down to room temperature, the reaction product is recovered by centrifugation, washed twice with 1600 ml of deionized water, and then collected, dried in a 60°C oven for 12 hours to obtain nano-Na/Fe composite solid acid catalyst.

Using cellulose as the raw material for catalytic pyrolysis, cellulose and nano-Na/Fe composite solid acid catalyst were placed in a fixed bed reactor with a diameter of 45 mm and a length of 60 mm in a mass ratio of 1:10 for mixed pyrolysis. The pyrolysis reaction is carried out under the atmosphere (helium 99.999%), the pyrolysis temperature is 550°C, the heating rate is 300°C/min, and the reaction time is 20min, so that the mixture is fully decomposed, and the pyrolysis volatiles are brought into the condensation by the inert gas helium. Condensation in the vessel to obtain furfural liquid product.

Figure 1a is an SEM image of the catalyst prepared in Example 1. It can be seen from the figure that the catalyst has a uniform size, is spherical, has a diameter of about 4.2 nm and is relatively uniformly dispersed.

Example 2

This example is the same as Example 1, except that the amount of NaOH added is prepared at a final Na/Fe mass ratio of 0.36, and other conditions are the same as Example 1.

Fig. 1b is an SEM image of the catalyst prepared in Example 2, and it can be seen from the figure that the catalyst has a rod-like structure.

Example 3

This example is the same as Example 1, except that the amount of NaOH added is prepared at a final Na/Fe mass ratio of 0.69, and other conditions are the same as Example 1.

Fig. 1c is an SEM image of the catalyst prepared in Example 3, and it can be seen from the figure that the morphology of the catalyst is a prismatic structure.

Example 4

This example is the same as Example 1, except that the amount of NaOH added is prepared at a final Na/Fe mass ratio of 2.31, and other conditions are the same as Example 1.

Fig. 1d is an SEM image of the catalyst prepared in Example 4, and it can be seen from the figure that the morphology of the catalyst is a highly aggregated structure.

According to Figure 1, it can be seen that the morphology of the catalyst can be changed by changing the Na/Fe mass ratio in the solution, including rod-shaped, prismatic, spherical and aggregated shapes, in which the spherical shape catalyst is uniformly dispersed.

Figure 2 is the nitrogen adsorption and desorption curve diagram of the catalyst prepared in Example 1-4 of the present invention. As shown in Figure 2, the catalyst in Example 2-4 mainly exists in mesopores, and the catalyst in Example 1 is composed of mesopores and The hierarchical pore structure with the coexistence of micropores has a specific surface area as high as 201.4 m ² /g (see Table 1), indicating that the spherical catalyst has high active sites.

Table 1 Pore characteristics of Na/Fe composite solid acid catalysts

Fig. 3 is the ion chromatogram after the original pyrolysis of cellulose, Fig. 4 is the ion chromatogram after the catalytic pyrolysis of cellulose and the catalyst prepared in Example 1 (mass ratio 1:10), it can be seen from Fig. 4 Compared with pure pyrolysis of cellulose, the furfural peak area of catalytic pyrolysis products increased by more than 20 times.

Example 5

The catalyst preparation part in this example is the same as that in Example 1. Hemicellulose is used as the raw material for pyrolysis, and cellulose and nano-Na/Fe composite solid acid catalyst are placed in a 45mm diameter and 60mm long composite solid acid catalyst in a mass ratio of 1:10. The fixed bed reactor conducts mixed pyrolysis, and the pyrolysis reaction is carried out under an inert atmosphere (helium 99.999%), the pyrolysis temperature is 550 ° C, the heating rate is 300 ° C/min, and the reaction time is 20 min, so that the mixture is fully decomposed, and the heat The volatile matter is brought into the condenser by the inert gas helium to be condensed to obtain the furfural liquid product.

Figure 5 is the GCMS spectrum of the pyrolysis liquid product of Example 5. It can be seen from the figure that the selectivity of furfural is as high as 99%, and the catalyst realizes the directional depolymerization and hydrolysis of hemicellulose to generate furfural.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (9)

1. a nanometer Na/Fe composite solid acid catalyst preparation method, is characterized in that, comprises the steps: S1 Weigh FeCl ₃ ·6H ₂ O and FeCl ₂ ·4H ₂ O of required quality, put them in deionized water and stir evenly to form a clear solution, add hydrochloric acid and stir; among them, FeCl ₃ ·6H ₂ O and FeCl ₂ ·4H ₂ O is prepared according to the mole fraction ratio of Fe ³⁺ : Fe ²⁺ as 2:1; S2 was gradually dripped with NaOH solution under stirring by a stirrer to produce a red-black precipitate, and the dripping was terminated when the pH of the solution was 2-6, and the constant speed stirring was continued, and then it was allowed to stand for a period of time to reduce to room temperature; wherein, the concentration of the NaOH solution was 1mol/L～2mol/L, the dosage of NaOH solution is prepared with the mass ratio of Na/Fe in the total solution as (0.05～2.5):1; The reaction product was recovered by centrifugation in S3, washed with deionized water for several times, and then collected, and then dried in an oven to obtain a nano-Na/Fe composite solid acid catalyst. 2. The catalyst preparation method according to claim 1, characterized in that, in step S2, the amount of NaOH solution is prepared with a Na/Fe mass ratio of 1.42:1 in the total solution. 3. The catalyst preparation method according to claim 1, characterized in that, in step S2, the stirring temperature is kept at 60°C, the stirring speed is kept at 600-1000r/min, and the stirring time is 1h after the dripping is finished, and the static Set time is 30 ~ 60min. 4. The catalyst preparation method according to claim 1, wherein in step S3, the centrifugal rotation speed is 3000-4000 r/min, and the number of times of washing with deionized water is 2-5 times. 5. The catalyst preparation method according to claim 1, wherein in step S3, the oven temperature is 60°C, and the drying time is 12-24h. 6. A nano-Na/Fe composite solid acid catalyst, characterized in that, prepared by the method of any one of claims 1-5. 7. a method for preparing furfural from biomass, it is characterized in that, after biomass raw material is mixed with the catalyst described in claim 6, it is placed in a pyrolysis furnace for pyrolysis, and the pyrolysis gas is condensed and collected to obtain a liquid enriched with furfural. product. 8. The method for preparing furfural from biomass as claimed in claim 7, wherein the pyrolysis reaction is carried out under an inert atmosphere, the pyrolysis temperature is 400～800 ℃, the temperature rise rate is 200～400 ℃/min, and the reaction time 20 to 30 minutes. 9. the method for preparing furfural from biomass as claimed in claim 7, is characterized in that, biomass raw material is one or more in cellulose, hemicellulose, agricultural waste, forestry waste, biomass raw material and The mass ratio of the catalyst was 1:10.

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